Dissecting the molecular mechanisms of producing biofuel and value-added products by cadmium tolerant microalgae as sustainable biorefinery approach

Microalgae can reconcile the deteriorating outcomes of environmental pollution by conserving the carbon footprint and generating green energy. Among different pollutants, cadmium (Cd) is one of the most noxious heavy metals that travels the ecological chain via phytoplanktons and stagnates the nutritional quality of aquatic life. In the present study, Scenedesmus sp. IITRIND2, a reported Cd-tolerant algal strain, has been subjected to detailed molecular investigations through metabolomics, gene expression, and biochemical analysis to dissect the pathways involved in Cd tolerance and the carbon flux channelization resulting in enhanced lipid/extracellular polysaccharide (EPS) production. The metabolic rewiring in the tricarboxylic acid (TCA) intermediates, amino acid metabolism, and starch metabolism presented the robust machinery of the cells to channelize the carbon pools for producing neutral lipids of vehicular quality under Cd stress. Further, microalgal cells instigated a defense network comprising organic osmolytes (betaine, ethylene glycol, sugars), antioxidants (glutathione, ascorbate, etc.,) and amino acids (glycine, glutamate, alanine, valine, threonine) suggesting the interplay of glutathione-ascorbate and probable phytochelatin based detoxification pathways as double edge sword to impart tolerance and detoxification of Cd. Moreover, stress-induced response constituted significant changes in the membrane fluidity and production of biodiesel quality lipids along with soluble EPS having paramount biotechnological applications. The outcomes of this study altogether presented an efficient model of algal-based biorefinery approach integrating the process of heavy metal (Cd) remediation and production of biodiesel and value-added products that are essential for a sustainable and circular economy.